1. Field of the Invention
The present invention relates to an information read out apparatus and, more paticularly, to an apparatus and method for reading information from a transferred information carrier with accuracy and without the necessity of strong transferring power for the information carrier.
2. Description of the Prior Art
As is well known, a image read out apparatus of the type using a contact image sensor is used in facsimile transmitters and other image scanners. The typical read out apparatus is shown in FIG. 1 and described in Applicant's Japanese Utility Model Publication No. U57-30673 published on July 6, 1982.
In the typical apparatus, document paper 1 is guided by guide plates 3 and transferred toward a nip between platen roller 2 and transparent plate 4 by transfer rollers not shown. Platen roller 2 is urged by springs toward transparent plate 4 arrow F in FIG. 1 shows the direction of the depression. Platen roller 2 also rotates simultaneously with the transfer rollers to transfer document paper 1, and the transferring speeds of the transfer rollers and platen roller 2 are equal to each other. Light source 5 radiates light to surface 1a of transferred document paper 1 through transparent plate 4 fixed on housing 8 by screws etc. The radiated light is reflected by surface 1a. Self-focusing rod-lens-array 6 receives the reflected light corresponding to information on document paper 1. The length of rod-lens-array 6 is greater than the width (210 mm) of the A4 size document 1 and the height of rod-lens-array 6 is usually 20 mm-50 mm in order to achieve the proper depth of focus. (The greater the height of self-focusing rod-lens-array, the greater the depth of focus.) The focal point A of rod-lens-array 6 is adjusted just on the surface of transparent plate 4. The reflected light from document paper 1 is received by photo-sensitive array 7, such as a CCD (Charge Coupled Device) array, to obtain electrical signals representing one line image. The electrical signals are transported to external circuitry (not shown in FIG. 1) to transmit another facsimile via a telephone line. Light source 5, self-focusing rod lens array 6 and CCD array 7 are arranged in the box comprising a housing and transparent plate 4.
In the typical apparatus, since platen roller 2 is always urged toward transparent plate 4, it contacts transparente plate 4 when paper 1 is not disposed between platen roller 2 and transparent plate 4. The frictional force between platen roller 2 and transparent plate 4 become great when there is no document paper 1 between platen roller 2 and transparent plate 4. This is due to the fact that platen roller 2 is made of rubber making it necessary for the step motor of platen roller 2 to have strong transferring power. Usually, the more the motor has the stronger the transffering power, the larger and more expensive the motor. Thus, it is difficult to manufacture a compact information reading out device because the motor of the platen roller 2 is large. Using a motor having strong transferring power also increases the cost of production. Further, since document paper 1 always is depressed against transparent plate 4, both surfaces of transparent plate 4 and platen roller 2 tend to become dirty if document paper 1 is stained. If transparent plate 4 become dirty, the light received by CCD array 7 contains an unnecessary image due to the stain. Thus, it is difficult to obtain good quality image light in the typical apparatus. If platen roller 2 and transparent plate 4 become dirty, an operator or a technician needs to remove the stain.